Methods: :
Retinal function was assessed with the full-field dark-adaptedelectroretinogram before, during and after IOP elevations of30, 45 or 60 mm Hg produced by reservoir cannulation of theanterior chamber of anesthetized Brown Norway rats. The ScotopicThreshold Response (STR) was used to assess inner-retinal function(-4.7 log sc.cd/m2) and scotopic a- and b-waves were used toassess rod photoreceptor and bipolar cell function (1.7 logsc.cd/m2). The duration of IOP elevation chosen for each pressurewas different so that they all yielded an IOP integral (pressurex duration) of 5250 mm Hg-minutes. Control and recovery phaseswere also measured for 30 minutes prior to and 80 minutes afterIOP elevations, respectively, at an IOP of 10 mm Hg.

Results: :
Reductions in a- & b-waves and STR were seen at 60 mm Hg,whereas only the STR was reduced at 30 and 45 mm Hg. The magnitudeof STR reduction was greater with increasing IOP integral witha greater reduction observed for the higher IOP at each integral(30 mm Hg: slope=-0.004, r=0.9, p<0.0001, 45 mm Hg: slope=-0.009,r=0.94, p<0.0001). The STR was reduced by 26 and 55% for30 and 45 mm Hg respectively at the maximum IOP integral of5250 mm Hg-minutes. When IOP was returned to baseline the STRshowed 36% recovery by 80 minutes for eyes held at 45 mm Hg.But, no obvious recovery was seen for eyes held at 30 mm Hg.

Conclusions: :
Inner-retinal responses can be selectively reduced for acuteelevation of IOP in the range of 30-45 mm Hg if IOP elevationsare maintained for sufficiently long durations. In this nominalpressure range, while peak IOP may be the more important determinantof the magnitude of functional loss, the duration of IOP elevationmay be a more important factor for functional recovery.